Dry plate rectifier assemblies



May 26, 1959 L. J. LOCKETT 2,883,618

DRY PLATE RECTIFIER ASSEMBLIES Filed Jan. 11, 1955 United States Patent Ofiice DRY PLATE RECTIFIER ASSEMBLIES,

Leslie Joseph Lockett, Kings Cross, London, England, assignor to Westinghouse Brake & Signal Company Limited, London, England Application January 11, 1955, Serial No. 481,172

Claims priority, application Great Britain January 13, 1954 3 Claims. (Cl. 317-234) This invention relates to dry plate rectifier assemblies, in particular to assemblies which have a high impedance.

It is known that high impedance elements or a size convenient for handling may be produced by limiting the area of the counter-electrode to a fraction of that of the element. With such an arrangement, however, difiiculty is encountered in ensuring that contact is made during assembly between the counter-electrode and the external electric circuit.

It is known also that such difiiculties may be overcome in part by employing a rectifier assembly of the kind in which a rectifier element and a contact member are enclosed Within an insulating tube, the rectifier element and the contact member having portions which co-operate with the interior surface of the tube to locate them centrally within the tube, the contact member having another portion which extends axially along the tube in the direction of the element, the element and the contact member being maintained in contact with each other by spring pressure.

One object of the invention is to provide an assembly of the kind described which is suitable for large scale production in that the number of parts, and therefore the number of contacts in series, is reduced to a minimum.

Another object of the invention is to permit the use of a tube of ceramic or similar hard material if so desired, of a uniform cross section such as may conveniently be produced by an extrusion process, and yet avoid the difliculties usually encountered in securing thereto suitable end-closure members capable of retaining the assembly in position against the spring pressure above mentioned.

Another object of the invention is to provide an assembly which may be soldered into an electric circuit without risk of the rectifying element being damaged' by heat conducted from the soldered joint.

According to the invention, in a rectifier assembly of the kind described the spring pressure is provided by means of at least one helical spring formed of electrically conducting wire or strip and having a portion of large diameter and a portion of small diameter, said spring being retained within the insulated tube by resilient engagement of the portion of large diameter with the inner surface of the tube, the portion of small diameter extending towards the element.

Preferably the wire or strip of which the spring is formed has a portion which projects beyond the tube to form a means for connecting the assembly to an electric circuit. Preferably, also, the spring may be of such a length and be formed of material of such a cross section and low thermal conductivity as to permit the projecting portion to be soldered without danger of heat conducted from the soldered joint causing damage to the element.

The tube may have a circular cross section and the contact member be a ball of slightly smaller diameter than that of the bore of the tube.

a rectifier element 2 and a copper spacer 3 are. retained between two Phosphor bronze springs 4 and 5 within a tube of insulating material 6, the pressure of the springs maintaining the ball in contact with a counter-electrode formed on one face of the element 2. Each spring is formed as a conical helix having a larger portion composed of about four coils whose respective outside diameters are larger than the diameters of the remaining coils and also slightly larger than the minimum interior dimension of the tube, i.e. the internal diameter in the case of the illustrated embodiment. The wire forming each spring is extended outwardly along the axis of the tube to form a connecting wire 7, 8 for connection to an electric circuit. The springs are inserted within the tube by winding them up sufficiently to reduce the diameter of the larger portion to a value which is less than that of the bore of the tube. The springs are then released, whereupon they expand to engage firmly the interior surface of the tube with their largest coils, leaving their smaller portion free to maintain pressure upon the assembly the reaction of such pressure upon the larger coils tending further to expand the latter and augmenting their grip within the bore of the tube.

One end of the tube is then closed by a metallic disc 9 and a suitable plastic potting compound such as Epikote (registered trademark) is injected at the other end, the plastic compound flowing through a small clearance around the rectifier element and the ball until the tube is completely filled. The other end of the tube is then closed by a second metallic disc 10.

It will be understood that the contact member is not restricted to a spherical shape but may, for instance, be formed as a solid of revolution having a portion of its surface projecting towards the counter-electrode. Further, the insulating tube is not restricted to having a circular cross section, but may have any section which permits accurate alignment of the contact member and the counter-electrode. Preferably three or more longitudinal ribs (not shown) are formed on the interior surface of the tube, the ribs ensuring accurate location of the various members Within the tube and the space between the ribs providing a large clearance through which resin may flow.

It will also be understood that the end closures may be of insulating material.

Having thus described my invention what I claim is:

l. A rectifier assembly comprising a tube of insulating material, a rectifier element and a contact member both located Within said tube, at least one helical spring of electrically conductive material adapted to exert pressure maintaining contact between said rectifier element and said contact member, said spring having at least one coil which, in the free condition of the spring, is of an outside diameter larger than that of the remaining coils and also slightly larger than the minimum interior dimension of said tube so as to retain the spring within the tube by resilient engagement with the interior surface thereof, the remaining coils of said spring extending towards said rectifier element. a

2. A rectifier assembly comprising a tube of insulating material, a rectifier element and a contact member both located within said tube, at least one helical spring of electrically conductive material adapted to exert pressure maintaining contact between said rectifier element and said contact member, and a connecting wire formed integrally with said spring and extending beyond said tube, said spring having at least one coil which, in the free condition of the spring, is of an outside diameter larger than that of the remaining coils and also slightly Patented May 26, 19.59.-

References Cited in the file of this patent UNITED STATES PATENTS Utne May 16, Ruben Nov. 7, Skinker Nov. 30, Bonner M Jan. 25, Ostapkovich July 12, 

